1. Field of the Invention
The present invention relates in general to an ink-jet recording apparatus which performs recording or printing by ejecting ink droplets.
2. Discussion of Related Art
An ink-jet head of an ink-jet printer for ejecting ink droplets onto a recording medium such as a recording sheet includes: a flow-passage unit in which are formed nozzles through which ink droplets are ejected and pressure chambers which communicate with the nozzles; actuators which apply an ejection energy to ink in the pressure chambers; and a driver IC in which are incorporated signal output circuits which output drive signals for driving the actuators. As the actuators each configured to apply a pressure to the ink in the pressure chambers by changing the volume thereof, there is known one disclosed in Patent Document 1 including: a piezoelectric sheet (piezoelectric layer) extending over a plurality of pressure chambers; a plurality of individual electrodes facing respectively the plurality of pressure chambers; and a common electrode (ground electrode) which faces the plurality of individual electrodes via the piezoelectric sheet and to which a base potential is given. In the disclosed actuators, when a drive pulse signal outputted from the signal output circuit of the driver IC is inputted to one of the individual electrodes, an electric field is generated at a portion of the piezoelectric sheet interposed between the above-indicated one individual electrode and the common electrode in a thickness direction of the piezoelectric sheet, so that the piezoelectric sheet at that portion expands or elongates in the thickness direction. Accordingly, the volume of the pressure chamber that corresponds to the one individual electrode is changed, whereby the pressure (ejection energy) is given to the ink in that pressure chamber.
In the driver IC, transistors and protective diodes of each signal output circuit are degraded due to latch-up, a surge arising from electrostatic discharge, etc., so that a leak current is generated. Heat generated by the leak current may break the signal output circuit. When an abnormality occurs in the signal output circuit, it is impossible to sufficiently apply an electric field to the piezoelectric sheet, so that the actuator cannot be driven at a high speed. Meanwhile, in each actuator, the piezoelectric sheet may suffer from a crack occurred therein. In this instance, the displacement amount of the piezoelectric sheet is reduced, thereby reducing the drive force of the actuator. If the actuator is continuously driven with the crack occurred in the piezoelectric sheet, the crack is enlarged, so that the ink enters the inside of the actuator through the crack, causing a risk of generating a short circuit in the actuator and the wiring connected thereto.
To monitor an abnormality in the driver IC and the actuators, there has been proposed, in Patent Document 2, a technique of monitoring an electric current in each signal output circuit by providing an electric current detecting circuit for each of the signal output circuits that correspond to the respective actuators.
Patent Document 1 JP 2002-36568 (FIG. 1)
Patent Document 2 JP 2002-127405 (FIG. 1)